Canopy question...

[Super_Dave]

The weather in Oreygon can get wet once in a while and I want to be able to hall sheet goods for the shop and keep them dry, so I want to add a nice, clean used canopy that will fit my overall build on my '74 C20.

So, being new to canopy's, how "specific" are canopies to the specific truck make and model? For instance, are the canopy's for the 73-87 years specific to that range... or will the 88 and newer model years still "fit?" I guess the essential issue is at what point did the cab profile change making the year range a critical issue?

I know I can chat up the manufacturers or dealers, but I don't want to always fight their selling efforts, since I will be looking for a used one.

Thanks!